Concentration-modulated coatings

ABSTRACT

The invention provides a substrate bearing a low-emissivity coating. The low-emissivity coating comprises at least one graded film region. In certain embodiments, at least one graded film region is provided between the two infrared-reflective layers of a double-type low-emissivity coating. The graded film region has a substantially continuously decreasing concentration of a first dielectric material and a substantially continuously increasing concentration of a second dielectric material. Also provided are methods of depositing such low-emissivity coatings and substrates bearing these coatings.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 10/876,254, which in turn claims priority to U.S.patent application No. 60/482,128, filed Jun. 24, 2003, the entiredisclosure of each which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention provides coatings for glass and other substrates.More particularly, this invention provides low-emissivity coatings. Alsoprovided are methods of depositing low-emissivity coatings andsubstrates bearing these coatings.

BACKGROUND OF THE INVENTION

Low-emissivity coatings are well known in the present art. Typically,they include one or more infrared-reflective layers each positionedbetween two or more dielectric layers. The infrared-reflective layersreduce the transmission of radiant heat through the coating. Theinfrared-reflective layers typically comprise electrically-conductivemetals, such as silver, gold, or copper. The dielectric layers reducethe visible reflectance of the coating and control other coatingproperties, such as color. Commonly used dielectrics include oxides ofzinc, tin, and titanium, as well as nitrides, such as silicon nitride.

Manufacturers have historically provided a single, thick dielectriclayer on each side of each infrared-reflective layer. Reference is madeto U.S. Pat. No. 4,859,532, the entire contents of which areincorporated herein by reference. Thick dielectric layers, however, areless than ideal in several respects. For example, the stress in adielectric layer increases with increasing layer thickness. This isparticularly problematic with dielectric films that inherently have highstress, such as silicon nitride. Further, it has been discovered thathaze formation is likely to occur in heat-treatable (e.g., temperable)coatings that comprise thick dielectric layers. U.S. patent applicationSer. No. 09/728,435, entitled Haze-Resistant Transparent Film Stacks,the entire contents of which are incorporated herein by reference,addresses this problem and replaces thick dielectric layers with aplurality of thin dielectric layers.

Typically, the dielectric layers in a low-emissivity coating arehomogenous. That is, each dielectric layer typically has a compositionthat is uniform over the thickness of the layer. While homogenousdielectric layers have gained widespread acceptance, they havesignificant limitations. For example, the adhesion properties arelimited for a low-emissivity coating wherein all the dielectric layersare homogenous. This is due in part to the discrete interfaces thatexist between homogenous dielectric layers. Stress tends to pile up(i.e., be concentrated) at each discrete interface in a low-emissivitycoating. Therefore, each such interface is a potential delamination sitethat is preferably avoided.

Further, the optical opportunities are limited for a low-emissivitycoating wherein all the dielectric layers are homogenous. A coating ofthis nature may only achieve limited color and antireflection propertiesdue to the optical limitations of having each dielectric layer in thecoating be homogenous.

As noted above, the primary optical function of the dielectric films ina low-emissivity coating is to antireflect the infrared-reflective film(e.g., silver) in the coating. The dielectric films, however, desirablyprovide additional functions. Consider a double-silver coatingcomprising a dielectric inner coat (between the substrate and the firstsilver layer), a dielectric middle coat (between the two silver layers),and a dielectric outer coat (further from the substrate than the secondsilver layer). Each of these coats preferably has specificcharacteristics, as do the inner and outer interfaces of each coat.

Insofar as the dielectric inner coat is concerned, the inner interfaceof this coat preferably provides good adhesion to the substrate. It isdesirable to assure the base coat adheres well to the substrate, as thiscoat serves as the foundation for the coating. In some cases, it is alsodesirable that the outer interface of the inner coat provide good growthconditions for silver film. The electrical conductivity (and hence theemissivity) of a silver film varies depending upon the particularsurface on which the silver is deposited. Thus, when a silver film isprovided directly over the dielectric inner coat, the inner coatdesirably has an outer interface that provides a good nucleation surfaceon which to grow silver film. In such cases, this outer interfacepreferably also adheres well to the overlying silver film. Further, theouter interface in such cases preferably immobilizes the overlyingsilver as much as possible (particularly during heat treatment). It isto be appreciated that in some cases a metal blocker film or anothernon-dielectric film is alternatively placed beneath a silver film toachieved desired durability and/or optical and/or insulating properties.The dielectric inner coat preferably prevents sodium ions and othermaterial from diffusing out of a glass substrate (i.e., it preferablyseals the glass). This is desirable to protect the first silver layeragainst being corroded from below.

Unfortunately, it is difficult to optimize all these properties using aninner coat formed by a single layer of any one material. As analternative, the inner coat can be formed of two or more discrete layersof different materials, each chosen to optimize one or more of thedesired coating properties. However, this leaves the inner coat with anadditional interface which, as noted above, is preferably avoided.

The situation is similar for the dielectric outer coat. For example, theouter coat preferably defines an inner interface that adheres well tothe underlying film (e.g., to the second silver layer or the secondblocker layer). The outer coat desirably contributes to the mechanicaland chemical durability of the coating. For example, the outer coatpreferably comprises a chemically durable material. Conjointly, theouter coat preferably defines a smooth outer surface, so as to reducethe coating's vulnerability to being physically abraded. Finally, theouter coat preferably comprises film that prevents moisture, oxygen, andother reactive agents from diffusing to the underlying silver(particularly during heat treatment and over time). This is desirable toprotect the second silver layer against being corroded from above. Aswith the inner coat, it is difficult to optimize all the desiredproperties with an outer coat formed by a single layer of one material,yet forming the outer coat of two or more discrete layers of differentmaterials yields an additional interface, which is preferably avoided.

With respect to the dielectric middle coat, it is particularly desirableto optimize the properties and functions of the dielectric film used inthis coat. This is due in part to the great thickness of the middlecoat. (The middle coat is characteristically thicker than the inner andouter coats.) It is particularly desirable, for example, to minimize thestress in the middle coat. This is preferably accomplished by limitingthe thickness of each layer in the middle coat. As noted above, thestress in a dielectric layer tends to increase with increasing layerthickness. Thus, by limiting the thickness of each layer in the middlecoat (or at least those layers comprising high stress material), stresscan be advantageously reduced.

It is also desirable to provide a middle coat that prevents defects fromgrowing over the entire thickness of the middle coat. This can beaccomplished by providing a middle coat that comprises a plurality ofdielectric layers. In such a middle coat, defects (e.g., pinholes andthe like) are less likely to propagate from one layer to another,especially when contiguous layers are formed of different materials.Thus, by providing a middle coat comprising a plurality of dielectriclayers, it is less likely that defects will grow across the entirethickness of the middle coat.

Further, it is advantageous to provide a middle coat that is resistantto the haze formation that can occur, e.g., during heat treatment. Thiscan be accomplished by providing a middle coat comprising a plurality ofparticularly thin dielectric layers, preferably formed of particularmaterials. While this solution has great benefit, it is less than idealin that it creates additional interfaces in the middle coat.

Still further, the middle coat preferably defines an inner interfacethat adheres well to the underlying film (e.g., to the first silverlayer or the first blocker layer). Conjointly, in cases where silver ispositioned directly over the middle coat, the outer interface of themiddle coat preferably provides good growth conditions for the overlyingsilver layer. In such cases, this outer interface preferably adhereswell to the overlying silver film and immobilizes the overlying silverfilm as much as possible.

It is extremely difficult to optimize all these properties using amiddle coat formed by a single layer of any one material. Thus, themiddle coat can alternatively be formed by a plurality of discretelayers of different dielectrics, each chosen to optimize one or moreproperties. This, however, is less than ideal in that it leaves themiddle coat with additional interfaces, which are preferably avoided.

It would be desirable to provide a low-emissivity coating that minimizesthe foregoing limitations and optimizes the foregoing properties andfunctions.

SUMMARY OF THE INVENTION

In certain embodiments, the invention provides a substrate bearing alow-emissivity coating. In these embodiments, the low-emissivity coatingcomprises, in sequence outwardly: a dielectric inner coat; a firstinfrared-reflective layer (e.g., comprising material that is highlyreflective of solar radiation); a concentration-modulated middle coatincluding a first graded film region having a substantially continuouslydecreasing concentration of a first dielectric material and asubstantially continuously increasing concentration of a seconddielectric material, wherein the first and second dielectric materialsare different materials; a second infrared-reflective layer (e.g.,comprising material that is highly reflective of solar radiation); and adielectric outer coat.

In certain embodiments, the invention provides a substrate bearing alow-emissivity coating. In these embodiments, the low-emissivity coatingcomprises, in sequence outwardly: a concentration-modulated inner coatincluding a first graded film region having a substantially continuouslydecreasing concentration of tin oxide and a substantially continuouslyincreasing concentration of zinc oxide (or zinc tin oxide), wherein thefirst graded film region extends from a tin oxide-rich inner area to azinc oxide-rich (or zinc tin oxide-rich) outer area; a firstinfrared-reflective layer (e.g., comprising material that is highlyreflective of solar radiation); a dielectric middle coat; a secondinfrared-reflective layer (e.g., comprising material that is highlyreflective of solar radiation); and a dielectric outer coat.

In certain embodiments, the invention provides a sputtering lineincluding at least three adjacent sputtering bays each adapted fordepositing dielectric film. At least one of these bays is a transitionbay equipped with two or more sputtering targets of which at least twocarry different sputterable materials. The first target in thetransition bay carries the same sputterable material as the last or onlytarget in the preceding (i.e., immediately preceding) bay. The lasttarget in the transition bay carries the same sputterable material asthe first or only target in the subsequent (i.e., immediatelysubsequent) bay.

In certain embodiments, the invention provides a method of producingcoated substrates. In these embodiments, the method comprises providinga sputtering line including at least three adjacent sputtering bays eachadapted for depositing dielectric film. At least one of these bays is atransition bay equipped with two or more sputtering targets of which atleast two carry different sputterable materials. The first target in thetransition bay carries the same sputterable material as the last or onlytarget in the preceding bay. The last target in the transition baycarries the same sputterable material as the first or only target in thesubsequent bay. The substrate is conveyed through the sputtering lineand the targets are sputtered to deposit upon the substrate a coatingcomprising a graded film region.

In certain embodiments, the invention provides a method of producingcoated substrates. In these embodiments, the method comprises depositinga low-emissivity coating upon a substrate, the coating comprising, insequence outwardly: a dielectric inner coat; a first infrared-reflectivelayer comprising material that is highly reflective of solar radiation;a concentration-modulated middle coat including a first graded filmregion having a substantially continuously decreasing concentration of afirst dielectric material and a substantially continuously increasingconcentration of a second dielectric material, wherein the first andsecond dielectric materials are different materials; a secondinfrared-reflective layer comprising material that is highly reflectiveof solar radiation; and a dielectric outer coat. In some cases, theconcentration-modulated middle coat is deposited as film having an indexof refraction that is substantially uniform across an entire thicknessof the middle coat. For example, the concentration-modulated middle coatcan be deposited as film having an index of refraction of between about1.9 and about 2.2. Preferably, the concentration-modulated middle coatis deposited as film wherein there is no discrete interface betweenhomogenous dielectric layers. In some cases, the concentration-modulatedmiddle coat is deposited as film wherein there is no homogenous filmregion having a thickness of 200 angstroms or more. Preferably, thefirst graded film region is deposited as film wherein the concentrationof the first dielectric material decreases gradually as theconcentration of the second dielectric material increases gradually. Insome cases, the first dielectric material is tin oxide and the seconddielectric material is zinc oxide, and wherein the first graded filmregion is deposited so as to extend from a tin oxide-rich inner area toa zinc oxide-rich outer area. In these cases, the tin oxide-rich innerarea can be deposited directly over a first blocker layer, and the firstblocker layer can be deposited directly over the firstinfrared-reflective layer. This zinc oxide-rich outer area can bedeposited as film comprising at least about 40 angstroms of essentiallypure zinc oxide directly beneath the second infrared-reflective layer,and the second infrared-reflective layer can be deposited as filmcomprising silver. In some cases, the concentration-modulated middlecoat is deposited as film comprising, in a contiguous sequence movingoutwardly: a first high concentration area, the first high concentrationarea being rich in the first dielectric material; the first graded filmregion; a second high concentration area, the second high concentrationarea being rich in the second dielectric material; a second graded filmregion having a substantially continuously decreasing concentration ofthe second dielectric material and a substantially continuouslyincreasing concentration of a third dielectric material, wherein thesecond and third dielectric materials are different materials; and athird high concentration area, the third high concentration area beingrich in the third dielectric material. In these cases, the thirddielectric material can be zinc oxide, such that the third highconcentration area is deposited as a zinc oxide-rich area. This zincoxide-rich area can be deposited as film comprising at least about 40angstroms of essentially pure zinc oxide directly beneath the secondinfrared-reflective layer, and the second infrared-reflective layer canbe deposited as film comprising silver. The first and third dielectricmaterials can both the same material, if so desired, such that the firstand third high concentration areas are both deposited as film rich inthe same material. For example, the first and third dielectric materialscan both be zinc oxide, such that the first and third high concentrationareas are both deposited as zinc oxide-rich areas. Further, the seconddielectric material can be deposited as an oxide selected from the groupconsisting of tin oxide, zinc tin oxide, and titanium oxide. In somecases, the first high concentration area is deposited as film comprisinga first homogenous film region consisting essentially of the firstdielectric material, the second high concentration area is deposited asfilm comprising a second homogenous film region consisting essentiallyof the second dielectric material, and the third high concentration areais deposited as film comprising a third homogenous film regionconsisting essentially of the third dielectric material. In these cases,each homogenous film region is preferably deposited at a thickness ofless than 200 angstroms. Further, the second homogenous film region ispreferably deposited at a thickness of less than about 180 angstroms. Insome cases, the concentration-modulated middle coat is deposited as filmcomprising, in a contiguous sequence moving outwardly: a first highconcentration area, the first high concentration area being rich in thefirst dielectric material; the first graded film region; a second highconcentration area, the second high concentration area being rich in thesecond dielectric material; a second graded film region having asubstantially continuously decreasing concentration of the seconddielectric material and a substantially continuously increasingconcentration of a third dielectric material, wherein the second andthird dielectric materials are different materials; a third highconcentration area, the third high concentration area being rich in thethird dielectric material; a third graded film region having asubstantially continuously decreasing concentration of the thirddielectric material and a substantially continuously increasingconcentration of a fourth dielectric material, wherein the third andfourth dielectric materials are different materials; a fourth highconcentration area, the fourth high concentration area being rich in thefourth dielectric material; a fourth graded film region having asubstantially continuously decreasing concentration of the fourthdielectric material and a substantially continuously increasingconcentration of a fifth dielectric material, wherein the fourth andfifth dielectric materials are different materials; and a fifth highconcentration area, the fifth high concentration area being rich in thefifth dielectric material. Preferably, the fifth dielectric material iszinc oxide, such that the fifth high concentration area is deposited asa zinc oxide-rich area. This zinc oxide-rich area can be advantageouslydeposited as film comprising at least about 40 angstroms of essentiallypure zinc oxide directly beneath the second infrared-reflective layer,and the second infrared-reflective layer can be advantageously depositedas film comprising silver. If so desired, the first, third, and fifthdielectric materials can all be the same material, such that the first,third, and fifth high concentration areas are all deposited as film richin the same material. For example, the first, third, and fifthdielectric materials can all be zinc oxide, such that the first, third,and fifth high concentration areas are all deposited as zinc oxide-richareas. Further, the second and fourth dielectric materials can both bethe same material, such that the second and fourth high concentrationareas are both deposited as film rich in the same material. For example,the second and fourth dielectric materials can both be deposited as anoxide selected from the group consisting of tin oxide, zinc tin oxide,and titanium oxide. In some cases, the first high concentration area isdeposited as film comprising a first homogenous film region consistingessentially of the first dielectric material, the second highconcentration area is deposited as film comprising a second homogenousfilm region consisting essentially of the second dielectric material,the third high concentration area is deposited as film comprising athird homogenous film region consisting essentially of the thirddielectric material, the fourth high concentration area is deposited asfilm comprising a fourth homogenous film region consisting essentiallyof the fourth dielectric material, and the fifth high concentration areais deposited as film comprising a fifth homogenous film regionconsisting essentially of the fifth dielectric material. Preferably,each homogenous film region is deposited at a thickness of less than 200angstroms. Further, the second and fourth homogenous film regions arepreferably each deposited at a thickness of less than about 180angstroms. In some cases, the dielectric inner coat is deposited as aconcentration-modulated inner coat comprising a second graded filmregion having a substantially continuously decreasing concentration of athird dielectric material and a substantially continuously increasingconcentration of a fourth dielectric material, wherein the third andfourth dielectric materials are different materials. Additionally (oralternatively), the dielectric outer coat can be deposited as aconcentration-modulated outer coat comprising a third graded film regionhaving a substantially continuously decreasing concentration of a fifthdielectric material and a substantially continuously increasingconcentration of a sixth dielectric material, wherein the fifth andsixth dielectric materials are different materials. In some cases ofthis nature, the concentration-modulated inner, middle, and outer coatsare each deposited as film not including any discrete interface betweenhomogenous dielectric layers.

In certain embodiments, the invention provides a method of producingcoated substrates. In these embodiments, the method comprises depositinga low-emissivity coating upon a substrate, the coating comprising, insequence outwardly: a concentration-modulated inner coat including afirst graded film region having a substantially continuously decreasingconcentration of tin oxide and a substantially continuously increasingconcentration of zinc oxide or zinc tin oxide, wherein the first gradedfilm region extends from a tin oxide-rich inner area to a zincoxide-rich or zinc tin oxide-rich outer area; a firstinfrared-reflective layer comprising material that is highly reflectiveof solar radiation; a dielectric middle coat; a secondinfrared-reflective layer comprising material that is highly reflectiveof solar radiation; and a dielectric outer coat. Preferably, the tinoxide-rich inner area of the first graded film region is deposited asfilm consisting essentially of tin oxide. In some cases, the tinoxide-rich inner portion of the first graded film region is depositeddirectly over the substrate. In other cases, the low-emissivity coatingfurther includes a base layer comprising silicon dioxide depositeddirectly over the substrate, the tin oxide-rich inner area of the firstgraded film region being deposited directly over the base layer.Preferably, the first infrared-reflective layer is deposited directlyover the outer area of the first graded film region. The outer area ofthe first graded film region can be advantageously deposited as filmcomprising at least about 40 angstroms of essentially pure zinc oxidedirectly beneath the first infrared-reflective layer, and the firstinfrared-reflective layer can be advantageously deposited as filmcomprising silver. In some cases, the concentration-modulated inner coatis deposited as film comprising, in a contiguous sequence movingoutwardly: a first high concentration area, the first high concentrationarea being rich in tin oxide; the first graded film region; a secondhigh concentration area, the second high concentration area being richin zinc oxide or zinc tin oxide; a second graded film region having asubstantially continuously decreasing concentration of zinc oxide orzinc tin oxide and a substantially continuously increasing concentrationof tin oxide; a third high concentration area, the third highconcentration area being rich in tin oxide; a third graded film regionhaving a substantially continuously decreasing concentration of tinoxide and a substantially continuously increasing concentration of zincoxide or zinc tin oxide; and a fourth high concentration area, thefourth high concentration area being rich in zinc oxide or zinc tinoxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially broken-away, schematic, cross-sectional side viewof a low-emissivity coating in accordance with certain embodiments ofthe present invention;

FIG. 2 is a broken-away, schematic, cross-sectional side view of amiddle portion of a low-emissivity coating in accordance with certainembodiments of the invention;

FIG. 3 is a broken-away, schematic, cross-sectional side view of amiddle portion of a low-emissivity coating in accordance with certainembodiments of the invention;

FIG. 4 is a schematic side view of a sputtering apparatus in accordancewith certain embodiments of the invention;

FIG. 5A is a schematic side view of a sputtering apparatus in accordancewith certain embodiments of the invention; and

FIG. 5B is a schematic side view of a sputtering apparatus in accordancewith certain embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description is to be read with reference to thedrawings, in which like elements in different drawings have likereference numerals. The drawings, which are not necessarily to scale,depict selected embodiments and are not intended to limit the scope ofthe invention. Skilled artisans will recognize that the examplesprovided herein have many useful alternatives that fall within the scopeof the invention.

Substrates of various size can be used in the present invention.Commonly, large-area substrates are used. Certain embodiments involve asubstrate having a width of at least about 0.5 meter, preferably atleast about 1 meter, perhaps more preferably at least about 1.5 meters(e.g., between about 2 meters and about 4 meters), and in some cases atleast about 3 meters.

Substrates of various thickness can be used in the present invention.Commonly, substrates (e.g., glass sheets) with a thickness of about 1-5mm are used. Certain embodiments involve a substrate with a thickness ofbetween about 2.3 mm and about 4.8 mm, and perhaps more preferablybetween about 2.5 mm and about 4.8 mm. In some cases, a sheet of glass(e.g., soda-lime glass) with a thickness of about 3 mm will be used.

In certain embodiments, the invention provides a substrate 10 bearing alow-emissivity coating 40. A variety of substrates are suitable for usein the present invention. In most cases, the substrate is a sheet oftransparent material (i.e., a transparent sheet). However, the substrateis not required to be transparent. For most applications, the substratewill comprise a transparent or translucent material, such as glass orclear plastic. In many cases, the substrate 10 will be a glass pane. Avariety of known glass types can be used, and soda-lime glass isexpected to be preferred.

In certain preferred embodiments, the low-emissivity coating 40comprises a concentration-modulated middle coat 90. Here, the coating 40includes two infrared-reflective layers 50, 150 (e.g., comprisingsilver) between which is positioned the concentration-modulated middlecoat 90. Certain embodiments of this nature are exemplified in FIG. 1,wherein the illustrated coating 40 comprises, in sequence outwardly(i.e., in sequence moving away from the substrate): a dielectric innercoat 30; a first infrared-reflective layer 50; an optional first blockerlayer 80; the concentration-modulated middle coat 90; a secondinfrared-reflective layer 150; an optional second blocker layer 180; anda dielectric outer coat 70. In these embodiments, the inner and outercoats can be formed of any desired dielectric films, includingconventional homogenous dielectric layers (i.e., non-graded layers).Alternatively, one or both of the inner and outer coats can also have agraded composition, as described below.

The concentration-modulated middle coat 90 can be provided in variousforms. Preferably, this middle coat 90 includes at least one graded filmregion. In other words, at least a portion of theconcentration-modulated middle coat preferably has a graded composition(e.g., a composition that changes gradually with increasing distancefrom the substrate). By providing the middle coat 90 with one or moregraded film regions, the coating 40 can be designed to achieve anexceptional range of color and antireflection properties. Further,special optical effects can be achieved using graded film. Moreover, thegraded composition of the concentration-modulated middle coat isdesirable in terms of low stress and good adhesion properties. Forexample, it eliminates discrete interfaces that would otherwise becandidates for delamination. In certain preferred embodiments, themiddle coat 90 does not include any (i.e., is entirely free of) discreteinterfaces between dielectric layers (e.g., between homogenousdielectric layers). For example, the entire middle coat 90 can bedesigned to have a gradually changing composition, with smoothtransition from one dielectric material to the next.

In more detail, the concentration-modulated middle coat 90 includes afirst graded film region having a substantially (or at least generally)continuously decreasing concentration of a first dielectric material anda substantially (or at least generally) continuously increasingconcentration of a second dielectric material. Here, the first andsecond dielectric materials are different materials. Thus, the gradedfilm region transitions (with increasing distance from the substrate)from one dielectric material to another dielectric material. Preferably,the concentration of the first dielectric material decreases graduallyas the concentration of the second dielectric material increasesgradually. Thus, there is preferably a smooth transition from onedielectric material to another. A middle coat 90 of this nature issuperior (in terms of stress, adhesion, and color and antireflectionopportunity) to a conventional middle coat formed by a plurality ofdiscrete homogenous layers.

Thus, the middle coat 90 desirably includes a graded film region havinga composition that transitions (as a function of film thickness) fromone dielectric material to another. A wide variety of dielectricmaterials can be used in the graded film region. The term “dielectric”is used herein to refer to any non-metallic (i.e., neither a pure metalnor a metal alloy) compound that includes any one or more metals. Incertain embodiments, each dielectric is a transparent dielectric that isgenerally or substantially transparent when deposited as a thin film.Included in the “dielectric” definition would be any metal oxide, metalnitride, metal carbide, metal sulfide, metal boride, and any combinationthereof (e.g., an oxynitride). Further, the term “metal” is to beunderstood to include all metals and semi-metals (i.e., metalloids).Useful metal oxides include oxides of zinc, tin, indium, bismuth,titanium, hafnium, zirconium, and mixtures thereof. While metal oxidesare desirable due to their ease and low cost of application, known metalnitrides (e.g., silicon nitride) can also be used. Skilled artisans willbe familiar with other useful materials.

With respect to the graded nature of the film, in preferred embodimentsthe film in each graded film region is graded in a common manner overthe entire area of the coated surface. Thus, at any given “x, y”location on the coated surface (where x and y are dimensions along tworespective perpendicular axes on the coated surface), there exists thegraded film (i.e., the described transition from one dielectric toanother). The “z” dimension (i.e., the film thickness dimension) rangeover which the graded film region exists may vary slightly from one x, ylocation to another, e.g., due to local variations in the surfaceroughness of the substrate. For example, this could result by sputteringthe coating over a glass substrate having preexisting surface roughness.

Preferably, the refractive index is substantially constant over thegraded film region. That is, the graded film region preferablytransitions from one dielectric material having a given refractive indexto another dielectric material having substantially the same refractiveindex. Generally, this refractive index is between about 1.9 and about2.75, preferably between about 1.9 and about 2.4, more preferablybetween about 1.9 and about 2.2, and perhaps optimally about 2.0. Inalternate embodiments, the refractive index of the film in the gradedfilm region varies, but not outside the range of 1.9-2.75, preferablynot outside the range of 1.9-2.4, and perhaps optimally not outside therange of 1.9-2.2.

In certain particularly preferred embodiments, the refractive index issubstantially constant over the entire thickness of theconcentration-modulated middle coat 90. Here, even though thecomposition of the middle coat 90 changes with increasing distance fromthe substrate (at least across a portion of the middle coat 90), therefractive index is substantially uniform across an entire thickness ofthe middle coat 90. This refractive index is generally between about 1.9and about 2.75, preferably between about 1.9 and about 2.4, morepreferably between about 1.9 and about 2.2, and perhaps optimally about2.0. In alternate embodiments, the refractive index of the film in themiddle coat 90 varies, but not outside the range of 1.9-2.75, preferablynot outside the range of 1.9-2.4, and perhaps optimally not outside therange of 1.9-2.2.

In certain favored embodiments, the concentration-modulated middle coat90 is formed entirely of oxide film, or of nitride film, etc. Forexample, the middle coat 90 can be deposited using a single reactive gastype (oxidizing, nitriding, etc.) It will be appreciated that impuritygases may also be present in small amounts during deposition, such thatthe middle coat may include trace impurities. Particularly favored aremethods wherein the middle coat includes at least one graded film regionand is deposited using only oxidizing atmosphere, such that the middlecoat is formed entirely of oxide film. Preferably, the middle coatincludes at least one film region comprising tin oxide or zinc tinoxide, both of which are particularly desirable due to, inter alia,their morphology.

In certain embodiments, the first and second dielectric materials aretwo different oxides selected from the group consisting of zinc oxide,tin oxide, zinc tin oxide (e.g., Zn₂SnO₄), zinc aluminum oxide (e.g.,ZnOAl₂O₃), and titanium oxide. Preferably, at least one of the first andsecond dielectric materials is tin oxide or zinc tin oxide. For example,the first and second dielectric materials can be two different oxidesselected from the group consisting of zinc oxide, tin oxide, and zinctin oxide. It is to be understood, however, that in other embodimentsany two dielectric materials can be used. For example, the first andsecond dielectric materials can be selected and varied to meet therequirements of many different applications.

Thus, the concentration-modulated middle coat includes at least onegraded film region characterized by a transition from one dielectricmaterial to another. In some cases, this middle coat includes only onegraded film region. In such cases, the second dielectric is preferablyzinc oxide, while the first dielectric is preferably an oxide selectedfrom the group consisting of tin oxide, zinc tin oxide, and titaniumoxide, perhaps optimally tin oxide or zinc tin oxide. In one embodiment,the first dielectric is tin oxide, and the first graded film regionextends from a tin oxide-rich inner area (adjacent the firstinfrared-reflective layer 50, e.g., over blocker layer 80 if provided)to a zinc oxide-rich outer area (adjacent the second infrared-reflectivelayer 150). Here, the tin oxide-rich inner area is preferably depositeddirectly over a first blocker layer 80, and the secondinfrared-reflective layer 150 is preferably deposited directly over thezinc oxide-rich outer area. This zinc oxide-rich outer area desirablycomprises at least about 40 Å of essentially pure zinc oxide directlybeneath the second infrared-reflective layer 150, at least if this layer150 comprises silver.

Thus, the middle coat 90 may comprise a single graded film regionextending from a tin oxide-rich inner area to a zinc oxide-rich outerarea. In such embodiments, the middle coat includes at least two highconcentration areas (the tin oxide-rich inner area is a first highconcentration area and the zinc oxide-rich outer area is a second highconcentration area). Each high concentration area is a thickness of filmhaving a local maximum concentration of a desired dielectric material.In some cases, each high concentration area has a major concentration(i.e., 50% or more) of the desired dielectric material. If so desired,each high concentration area can be a thickness of film consistingessentially of the desired dielectric material. For example, each highconcentration area can comprise a homogenous film region consistingessentially of the desired dielectric material.

Table 1 depicts an embodiment wherein the middle coat 90 comprises, in acontiguous sequence moving outwardly: (1) a first homogenous film regionconsisting essentially of tin oxide; (2) a first graded film regionhaving a substantially continuously decreasing concentration of tinoxide and a substantially continuously increasing concentration of zincoxide; and (3) a second homogenous film region consisting essentially ofzinc oxide. Here, the second homogenous film region desirably comprisesat least about 40 Å of essentially pure zinc oxide directly beneath thesecond infrared-reflective layer 150, which desirably is a silver film(but may simply include some silver or be an infrared-reflective filmthat does not contain silver, as may also be the case in any of thetables of the present disclosure).

The symbol “→” (i.e., an arrow) is used herein to refer to a change(e.g., a gradual change) in film composition, with increasing distancefrom the substrate, from the dielectric material identified at the baseof the arrow to the dielectric material identified at the tip of thearrow.

TABLE 1 glass/inner coat/silver/blocker/tin oxide→zincoxide/silver/blocker/ outer coat

Thus, in certain embodiments, the middle coat includes at least onehomogenous film region. The film in each homogenous film region does nothave a composition that is graded or otherwise varied as a function offilm thickness/distance from the substrate. Rather, each such region isa thickness of film having a homogenous composition (of a desireddielectric material). Preferably, each homogenous film region is boundedby (and transitions gradually into) one or two graded film regions. Incontrast, a conventional discrete homogenous dielectric layer is boundedby two discrete interfaces with other layers. In some cases, the middlecoat 90 includes a plurality of homogenous film regions, each formed ofa desired dielectric material. In these cases, each homogenous filmregion preferably has a thickness of less than 200 Å, and perhaps morepreferably less than about 180 Å, and perhaps optimally less than about175 Å. These thickness limits are desirable for minimizing stress,maximizing adhesion, limiting defect growth, and avoiding hazeformation, e.g., during heat treatment. Thus, in some embodiments, themiddle coat 90 does not include any homogenous film region having athickness of 200 Å or more.

Notwithstanding the foregoing, it is to be appreciated that the middlecoat 90 need not include any homogenous film region(s). For example, theinvention provides embodiments wherein the concentration of the entiremiddle coat 90 changes constantly with increasing distance from thesubstrate. In many embodiments, though, the middle coat comprises atleast one homogenous film region (e.g., at least about 40 angstroms ofessentially pure zinc oxide directly beneath the secondinfrared-reflective layer 150).

The invention provides several particularly desirable middle coatdesigns. A first design provides a middle coat 90 comprising two gradedfilm regions interposed among three high concentration areas.Embodiments of this nature are exemplified in FIG. 2. A second designprovides a middle coat 90 comprising three graded film regionsinterposed among five high concentration areas. Embodiments of thisnature are exemplified in FIG. 3. In FIGS. 2 and 3, each highconcentration area is identified by the reference character 90′ and eachrow of arrows identifies a graded film region. Each of these two designsyields an exceptional “double-type” low-emissivity coating (i.e., acoating having two infrared-reflective layers). For example, thesedesigns have a symmetrical configuration that yields exceptional opticalproperties.

In the first design, the concentration-modulated middle coat 90 includesthree high concentration areas and two graded film regions. For example,the middle coat 90 can comprise, in a contiguous sequence movingoutwardly: a first high concentration area; a first graded film region;a second high concentration area; a second graded film region; and athird high concentration area. Here, the first high concentration areais rich in a first dielectric material, the second high concentrationarea is rich in a second dielectric material, and the third highconcentration area is rich in a third dielectric material. The firstgraded film region has a substantially continuously decreasingconcentration of the first dielectric and a substantially continuouslyincreasing concentration of the second dielectric. The second gradedfilm region has a substantially continuously decreasing concentration ofthe second dielectric and a substantially continuously increasingconcentration of the third dielectric. In these embodiments, the firstand second dielectrics are different materials, and the second and thirddielectrics are different materials, however the first and thirddielectrics can be the same material. Preferably, at least one of thefirst, second, and third dielectric materials is tin oxide or zinc tinoxide.

In preferred embodiments of this nature, the third dielectric materialis zinc oxide, such that the third high concentration area is a zincoxide-rich area. Table 2 exemplifies such coatings. Preferably, thesecond infrared-reflective layer 150 comprises silver positioneddirectly over the zinc oxide-rich, third high concentration area, whichdesirably comprises at least about 40 Å of essentially pure zinc oxide.

In the embodiments of FIG. 2, the first and third dielectrics can bothbe the same material, such that the first and third high concentrationareas are both rich in the same material. In preferred embodiments ofthis nature, the first and third dielectrics are both zinc oxide suchthat the first and third high concentration areas are both zincoxide-rich areas. In these embodiments, the second dielectric materialdesirably is an oxide selected from the group consisting of tin oxide,zinc tin oxide, zinc aluminum oxide, and titanium oxide, preferably tinoxide or zinc tin oxide.

In some cases, the first, second, and third high concentration areas 90′all comprise homogenous film regions. That is, the first highconcentration area comprises a first homogenous film region consistingessentially of a first dielectric material, the second highconcentration area comprises a second homogenous film region consistingessentially of a second dielectric material, and the third highconcentration area comprises a third homogenous film region consistingessentially of a third dielectric material. In these embodiments, eachhomogenous film region desirably has a thickness of less than 200 Å.Conjointly, the second homogenous film region desirably has a thicknessof less than about 180 Å.

TABLE 2 glass/inner coat/silver/blocker/zinc oxide→tin oxide→zincoxide/silver/blocker/outer coat glass/inner coat/silver/blocker/zincoxide→zinc tin oxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc oxide→zinc aluminum oxide→zincoxide/silver/blocker/outer coat glass/inner coat/silver/blocker/zincoxide→titanium oxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc tin oxide→tin oxide→zincoxide/silver/blocker/outer coat glass/inner coat/silver/blocker/zinc tinoxide→zinc aluminum oxide→zinc oxide/silver/blocker/outer coatglass/inner coat/silver/blocker/zinc tin oxide→titanium oxide→zincoxide/silver/blocker/outer coat glass/inner coat/silver/blocker/zincaluminum oxide→tin oxide→zinc oxide/silver/blocker/outer coatglass/inner coat/silver/blocker/zinc aluminum oxide→zinc tin oxide→zincoxide/silver/blocker/outer coat glass/inner coat/silver/blocker/zincaluminum oxide→titanium oxide→zinc oxide/silver/blocker/outer coat

In the embodiments of FIG. 3, the concentration-modulated middle coat 90includes five high concentration areas and four graded film regions.Here, the middle coat 90 comprises, in a contiguous sequence movingoutwardly: a first high concentration area; a first graded film region;a second high concentration area; a second graded film region; a thirdhigh concentration area; a third graded film region; a fourth highconcentration area; a fourth graded film region; and a fifth highconcentration area. In more detail, the first high concentration area isrich in a first dielectric material, the second high concentration areais rich in a second dielectric material, the third high concentrationarea is rich in a third dielectric material, the fourth highconcentration area is rich in a fourth dielectric material, and thefifth high concentration area is rich in a fifth dielectric material.The first graded film region has a substantially continuously decreasingconcentration of the first dielectric and a substantially continuouslyincreasing concentration of the second dielectric. The second gradedfilm region has a substantially continuously decreasing concentration ofthe second dielectric and a substantially continuously increasingconcentration of the third dielectric. The third graded film region hasa substantially continuously decreasing concentration of the thirddielectric and a substantially continuously increasing concentration ofthe fourth dielectric. The fourth graded film region has a substantiallycontinuously decreasing concentration of the fourth dielectric and asubstantially continuously increasing concentration of the fifthdielectric. In these embodiments, the first and second dielectrics aredifferent materials, the second and third dielectrics are differentmaterials, the third and fourth dielectrics are different materials, andthe fourth and fifth dielectrics are different materials. However, thefirst and fifth dielectrics can be the same material, the second andfourth dielectrics can be the same material, etc. Preferably, at leastone of the first, second, third, fourth, and fifth dielectric materialsis tin oxide or zinc tin oxide.

In preferred embodiments of this nature, the fifth dielectric materialis zinc oxide, such that the fifth high concentration area is a zincoxide-rich area. Table 3 exemplifies coatings of this nature.Preferably, the second infrared-reflective layer 150 comprises silverpositioned directly over the zinc oxide-rich, fifth high concentrationarea, which desirably comprises at least about 40 Å of essentially purezinc oxide.

In the embodiments of FIG. 3, the first, third, and fifth dielectricscan all be the same material, such that the first, third, and fifth highconcentration areas are all rich in the same material. In preferredembodiments of this nature, the first, third, and fifth dielectrics areall zinc oxide (i.e., the first, third, and fifth high concentrationareas are all zinc oxide-rich areas). Alternatively or additionally, thesecond and fourth dielectrics can both be the same material, such thatthe second and fourth high concentration areas are both rich in the samematerial. For example, the second and fourth dielectric materials canboth be an oxide selected from the group consisting of tin oxide, zinctin oxide, zinc aluminum oxide, and titanium oxide, perhaps optimallytin oxide or zinc tin oxide.

TABLE 3 glass/inner coat/silver/blocker/zinc oxide→tin oxide→zincoxide→tin oxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc oxide→zinc tin oxide→zinc oxide→zinc tinoxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc oxide→zinc aluminum oxide→zinc oxide→zincaluminum oxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc oxide→titanium oxide→zinc oxide→titaniumoxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc tin oxide→tin oxide→zinc tin oxide→tinoxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc tin oxide→zinc aluminum oxide→zinc tinoxide→zinc aluminum oxide→zinc oxide/silver/blocker/outer coatglass/inner coat/silver/blocker/zinc tin oxide→titanium oxide→zinc tinoxide→titanium oxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc aluminum oxide→tin oxide→zinc aluminumoxide→tin oxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc aluminum oxide→zinc tin oxide→zinc aluminumoxide→zinc tin oxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/zinc aluminum oxide→titanium oxide→zinc aluminumoxide→titanium oxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/tin oxide→zinc tin oxide→tin oxide→zinc tinoxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/tin oxide→zinc aluminum oxide→tin oxide→zincaluminum oxide→zinc oxide/silver/blocker/outer coat glass/innercoat/silver/blocker/tin oxide→titanium oxide→tin oxide→titaniumoxide→zinc oxide/silver/blocker/outer coat

In certain embodiments, the first, second, third, fourth, and fifth highconcentration areas all comprise homogenous film regions. That is, thefirst high concentration area comprises a first homogenous film regionconsisting essentially of a first dielectric material, the second highconcentration area comprises a second homogenous film region consistingessentially of a second dielectric material, the third highconcentration area comprises a third homogenous film region consistingessentially of a third dielectric material, the fourth highconcentration area comprises a fourth homogenous film region consistingessentially of a fourth dielectric material, and the fifth highconcentration area comprises a fifth homogenous film region consistingessentially of a fifth dielectric material. In these embodiments, eachhomogenous film region desirably has a thickness of less than 200 Å.Conjointly, the second and fourth homogenous film regions each desirablyhas a thickness of less than about 180 Å.

In one embodiment, the first dielectric material is zinc oxide, thesecond dielectric material is tin oxide, the third dielectric materialis titanium oxide (or zinc tin oxide), the fourth dielectric material istin oxide, and the fifth dielectric material is zinc oxide. In anotherembodiment, the first dielectric material is zinc oxide, the seconddielectric material is titanium oxide, the third dielectric material istin oxide (or zinc tin oxide), the fourth dielectric material istitanium oxide, and the fifth dielectric material is zinc oxide. Instill another embodiment, the first dielectric material is zinc oxide,the second dielectric material is zinc tin oxide, the third dielectricmaterial is tin oxide (or titanium oxide), the fourth dielectricmaterial is zinc tin oxide, and the fifth dielectric material is zincoxide. In yet another embodiment, the first dielectric material is zinctin oxide, the second dielectric material is tin oxide, the thirddielectric material is titanium oxide, the fourth dielectric material istin oxide, and the fifth dielectric material is zinc oxide. In stillanother embodiment, the first dielectric material is zinc tin oxide, thesecond dielectric material is titanium oxide, the third dielectricmaterial is tin oxide, the fourth dielectric material is titanium oxide,and the fifth dielectric material is zinc oxide. In yet anotherembodiment, the first dielectric material is tin oxide, the seconddielectric material is titanium oxide, the third dielectric material iszinc tin oxide, the fourth dielectric material is titanium oxide, andthe fifth dielectric material is zinc oxide. In a further embodiment,the first dielectric material is tin oxide, the second dielectricmaterial is zinc tin oxide, the third dielectric material is titaniumoxide, the fourth dielectric material is tin oxide, and the fifthdielectric material is zinc oxide. Many other variations will beapparent to skilled artisans.

It is particularly preferred to provide the coating 40 with aconcentration-modulated middle coat 90. The middle coat of a double-typelow-emissivity coating characteristically has a relatively greatthickness. For example, it is common for the middle coat to be at leastabout twice as thick as the inner coat and/or at least about twice asthick as the outer coat. As a result, the drawbacks associated withthick dielectric layers are particularly acute with respect to themiddle coat. It is thus particularly preferred, especially in terms ofreduced stress, to provide the middle coat with the graded filmregion(s) described above.

Various embodiments have been described wherein the coating 40 has aconcentration-modulated middle coat 90. In some of these embodiments,the coating is also provided with a concentration-modulated inner coat30. Here, the inner coat includes a graded film region having asubstantially continuously decreasing concentration of one desireddielectric and a substantially continuously increasing concentration ofanother desired dielectric. In embodiments of this nature, the coatingcan also be provided with a concentration-modulated outer coat. Here,the outer coat includes a third graded film region having asubstantially continuously decreasing concentration of one dielectricand a substantially continuously increasing concentration of anotherdielectric. In these embodiments, the concentration-modulated inner,middle, and outer coats preferably do not include any discreteinterfaces between homogenous dielectric layers.

Thus, the invention provides desirable embodiments wherein the coating40 includes a concentration-modulated inner coat 30, aconcentration-modulated middle coat 90, and a concentration-modulatedouter coat 70. Table 4 exemplifies coatings of this nature. Here, theterms “D1”, “D2”, etc. refer respectively to a first dielectricmaterial, a second dielectric material, etc. (D1 and D2 are differentmaterials, and so on, though, D1 and D3 can be the same material, etc.).As noted above, each arrow represents a film composition gradientwherein, with increasing distance from the substrate, the composition ofthe film transitions from one material (the material identified left ofthe arrow) to another material (the material identified right of thearrow). These embodiments do not require use of any particulardielectric materials. Rather, any desired dielectrics can be used.Certain dielectrics, however, are preferred. Preferably, all the film inthe base coat 30 is deposited using the same reactive gas type(oxidizing, or nitriding, etc.), such that the base coat consistsessentially of oxide film or nitride film, etc. This is also preferablefor the middle 90 and outer 70 coats, as it allows for particularlyconvenient deposition methods. In particularly preferred embodiments,the entire coating 40 does not (or at least the inner coat 30, themiddle coat 90, and the outer coat 70 do not) include any discreteinterfaces between homogenous dielectric layers.

TABLE 4 glass/D1→D2/silver/blocker/D3→D4/silver/blocker/D5→D6glass/D1→D2/silver/blocker/D3→D4→D5/silver/blocker/D6→D7glass/D1→D2/silver/blocker/D3→D4→D5→D6→D7/silver/blocker/ D8→D9glass/D1→D2→D3/silver/blocker/D4→D5→D6/silver/blocker/D7→D8glass/D1→D2/silver/blocker/D3→D4→D5/silver/blocker/D6→D7→D8

The invention provides a number of embodiments wherein the coatingcomprises a particularly desirable concentration-modulated inner coat.Here, the modulated inner coat has an inner area comprising tin oxideand an outer area comprising zinc oxide, zinc tin oxide, or zincaluminum oxide. In some embodiments of this nature, the coating 40 is adouble-type low-emissivity coating comprising, in sequence outwardly: aconcentration-modulated inner coat 30; a first infrared-reflective layer50; an optional first blocker layer 80; a dielectric middle coat 90; asecond infrared-reflective layer 150; an optional second blocker layer180; and a dielectric outer coat 70. Here, the middle and outer coatscan be formed of any desired dielectric films, including conventionalhomogenous dielectric layers. Alternatively, one or both of the middleand outer coats can have a graded composition, as noted above. In otherembodiments of this nature, the coating is a “single type”low-emissivity coating (i.e., a low-emissivity coating having a singleinfrared-reflective layer) comprising, in sequence outwardly: aconcentration-modulated inner coat; an infrared-reflective layer; anoptional blocker layer; and a dielectric outer coat. Here, the outercoat can be formed of any desired dielectric films, includingconventional homogenous dielectric layers. Alternatively, the outer coatcan have a graded composition.

Preferably, the concentration-modulated inner coat includes a firstgraded film region having a substantially continuously decreasingconcentration of tin oxide and a substantially continuously increasingconcentration of zinc oxide, zinc tin oxide, or zinc aluminum oxide.Table 5 exemplifies coatings of this nature. Here, the first graded filmregion has an inner area that is rich in tin oxide and an outer areathat is rich in zinc oxide, zinc tin oxide, or zinc aluminum oxide.Perhaps optimally, the outer area is rich in zinc oxide. An inner coatof this nature can be produced, for example, using the sputteringapparatus depicted in FIG. 5B. In embodiments of this nature, theinfrared-reflective layer 50 is desirably deposited directly over thezinc oxide-rich outer area of the inner coat. Conjointly, this zincoxide-rich outer area desirably comprises at least about 40 angstroms ofessentially pure zinc oxide, while the infrared-reflective layer 50desirably is a silver film.

TABLE 5 glass/tin oxide→zinc oxide/silver/blocker/middlecoat/silver/blocker/outer coat glass/tin oxide→zincoxide/silver/blocker/outer coat glass/tin oxide→zinc tinoxide/silver/blocker/middle coat/silver/blocker/outer coat glass/tinoxide→zinc tin oxide/silver/blocker/outer coat glass/tin oxide→zincaluminum oxide/silver/blocker/middle coat/silver/blocker/outer coatglass/tin oxide→zinc aluminum oxide/silver/blocker/outer coat

In the embodiments of Table 5, the tin oxide-rich inner area (whichpreferably consists essentially of tin oxide) can be deposited directlyover the substrate. Alternatively, the coating can further include atransparent base layer comprising silicon dioxide deposited directlyover the substrate (preferably at less than 100 Å, and perhaps optimallyat about 50 Å-100 Å). In such cases, the tin oxide-rich inner area ispreferably deposited directly over the silicon dioxide. Some preferredembodiments of this nature are exemplified by the first six coatings inTable 6. Other preferred embodiments are exemplified by the last sixcoatings in Table 6, wherein the silicon dioxide is deposited directlyover the substrate, and this silicon dioxide transitions to tin oxide,which subsequently transitions to zinc oxide, zinc tin oxide, or zincaluminum oxide. These embodiments provide an extraordinarily durablefoundation for the coating.

TABLE 6 glass/silicon dioxide/tin oxide→zinc oxide/silver/blocker/middlecoat/silver/blocker/outer coat glass/silicon dioxide/tin oxide→zinc tinoxide/silver/blocker/middle coat/silver/blocker/outer coat glass/silicondioxide/tin oxide→zinc aluminum oxide/silver/blocker/middlecoat/silver/blocker/outer coat glass/silicon dioxide/tin oxide→zincoxide/silver/blocker/outer coat glass/silicon dioxide/tin oxide→zinc tinoxide/silver/blocker/outer coat glass/silicon dioxide/tin oxide→zincaluminum oxide/silver/blocker/outer coat glass/silicon dioxide→tinoxide→zinc oxide/silver/blocker/middle coat/silver/blocker/outer coatglass/silicon dioxide→tin oxide→zinc tin oxide/silver/blocker/middlecoat/silver/blocker/outer coat glass/silicon dioxide→tin oxide→zincaluminum oxide/silver/blocker/middle coat/silver/blocker/outer coatglass/silicon dioxide→tin oxide→zinc oxide/silver/blocker/outer coatglass/silicon dioxide→tin oxide→zinc tin oxide/silver/blocker/outer coatglass/silicon dioxide→tin oxide→zinc aluminum oxide/silver/blocker/outercoat

In certain preferred embodiments, the invention provides aconcentration-modulated inner coat comprising in a contiguous sequencemoving outwardly: (i) a first high concentration area, the first highconcentration area being rich in tin oxide; (ii) a first graded filmregion having a substantially continuously decreasing concentration oftin oxide and a substantially continuously increasing concentration ofzinc oxide; (iii) a second high concentration area, the second highconcentration area being rich in zinc oxide; (iv) a second graded filmregion having a substantially continuously decreasing concentration ofzinc oxide and a substantially continuously increasing concentration oftin oxide; (v) a third high concentration area, the third highconcentration area being rich in tin oxide; (vi) a third graded filmregion having a substantially continuously decreasing concentration oftin oxide and a substantially continuously increasing concentration ofzinc oxide; and (vii) a fourth high concentration area, the fourth highconcentration area being rich in zinc oxide. An inner coat of thisnature can be produced, for example, using the sputtering apparatus ofFIG. 5A.

With respect to the infrared-reflective film, silver preferably is used.While other infrared-reflective metals (e.g., copper, gold, platinum,palladium, nickel, and alloys) can be used, silver provides the lowestemissivity and best color neutrality. In other cases, theinfrared-reflective film comprises material other than silver, but isentirely metallic or essentially metallic (comprising no more than oneatomic percent of non-metal material). Preferably, though, pure silveror substantially pure silver (comprising no more than five atomicpercent of other material) is used. This provides the lowest emissivitypossible. Each infrared-reflective film can, for example, be depositedby sputtering a silver target in an inert atmosphere. Eachinfrared-reflective film may have discrete inner and outer interfaceswith the underlying and overlying films, respectively. In a double-typelow-emissivity coating, for example, a first silver film may have adiscrete inner interface with an underlying inner coat 30 and a discreteouter interface with an overlying film (which may be a blocker layer 80or the middle coat 90), and a second silver film may have a discreteinner interface with an underlying middle coat 90 and a discrete outerinterface with an overlying film (which may be a blocker layer 180 orthe outer coat 70). These embodiments are preferred because, inter alia,they impart exceptionally low emissivity in the coating 40.

Preferably, the total physical thickness of the inner coat is less than200 angstroms. Each infrared-reflective (e.g., silver) film preferablyhas a physical thickness of between about 40 angstroms and about 190angstroms. In embodiments wherein the coating includes twoinfrared-reflective films, the middle coat desirably has a totalphysical thickness of between about 150 angstroms and abut 700angstroms. The total physical thickness of the outer coat, whether thecoating has one or more infrared-reflective layers, is preferablybetween about 100 angstroms and about 300 angstroms. It is to beunderstood, however, that the thickness ranges noted in this paragraphare merely preferred, and many embodiments are anticipated wherein theactual thicknesses will fall outside these ranges.

In certain embodiments, the coating includes one or more graded filmregion each transitioning from a first oxide of zinc and tin to a secondoxide of zinc and tin. For example, such a graded film region may beformed by sequentially conveying a substrate past the followingsputtering targets: a first target formed of pure or essentially puretin, a second target formed of a high tin content (e.g., about 40% tinor more) zinc-tin material, a third target formed of a low tin content(e.g., about 20% tin or less) zinc-tin material, and a fourth targetformed of pure or essentially pure zinc. A graded film region of thisnature can be used in the inner coat, the middle coat, or the outercoat.

The invention also provides desirable methods for producing coatedsubstrates. Generally, these methods involve depositing a coating 40that includes a dielectric inner coat 30, a dielectric middle coat 90,and a dielectric outer coat 70, at least one of which comprises a gradedfilm region. Various suitable coatings of this nature have beendescribed, and the present methods extend to the deposition of any ofthe described coatings.

The present methods preferably involve depositing graded film withoutproducing any abrupt change in film composition (such that thecomposition of the film in each graded film region has no suddendiscontinuity). Preferably, the graded film is deposited so as toprovide a gradual transition from one dielectric material to the next(as a function of film thickness/distance from the substrate). This isdesirably accomplished by a sputtering process that involves using acommon target material for the last target in a desired sputtering bayand for the first (or only) target in the subsequent bay, and by using acommon target material for the first target in the desired bay and forthe last (or only) target in the preceding bay. In certain embodiments,each sputtering bay is separated from each adjacent bay by at least onechamber wall. This wall characteristically defines a narrow passagethrough which substrates can be conveyed (e.g., over rollers or othersubstrate supports defining a path of substrate travel) from one bay tothe next. The present methods allow manufacturers to optimize theproperties of the dielectric inner, middle, and/or outer coats, whileavoiding discrete interfaces, where stress tends otherwise to pile up(i.e., be concentrated).

In certain embodiments, the method comprises conveying a substratethrough at least three adjacent sputtering bays each adapted fordepositing dielectric film (e.g., each containing a reactive sputteringatmosphere and/or a ceramic target). The term “adjacent sputtering bays”is used herein to refer to sputtering bays through which a substrate isconveyed sequentially without being passed through any other bay. Atleast one of these three bays is equipped with two or more sputteringtargets, of which at least two carry different sputterable materials.The first target in this bay (the “transition” bay) carries the samesputterable material as the last (or only) target in the preceding bay.The last target in the transition bay carries the same sputterablematerial as the first (or only) target in the subsequent bay. This isperhaps best understood with reference to FIGS. 4-5B. (It is to beunderstood that the targets in the transition bay are sputtered in acommon (i.e., shared) sputtering atmosphere.)

FIG. 4 depicts one particular sputtering apparatus that can be used todeposit a concentration-modulated middle coat 90. This arrangement ofsputtering targets can be used, for example, to produce the middle coatof the first coating in Table 3. Here, the substrate is conveyed throughtwo sputtering bays each equipped with two zinc targets. These two baysare preferably provided with an oxidizing atmosphere, as is preferred inall the bays. The innermost area of the middle coat is thus deposited asa first homogenous film region, which consists essentially of zincoxide. Next, the substrate is conveyed through a bay in which the firsttarget is zinc and the second target is tin. As the substrate movesthrough this bay (along the path of substrate travel 99), the substrateis exposed initially to a relatively great amount of zinc oxide flux,and is exposed to a gradually decreasing amount of zinc oxide flux and agradually increasing amount of tin oxide flux, and toward the end of thebay is exposed to a relatively great amount of tin oxide flux. Thus, afirst graded film region is deposited in this bay. The substrate is thenconveyed through a bay equipped with two tin targets. In these two bays,there is deposited a second homogenous film region, which consistsessentially of tin oxide. Next, the substrate is conveyed through a bayin which the first target is tin and the second target is zinc. A secondgraded film region is deposited in this bay. The substrate is thenconveyed through two sputtering bays each equipped with two zinctargets. In these two bays, there is deposited a third homogenous filmregion, which consists essentially of zinc oxide. Then, the substrate isconveyed through a bay in which the first target is zinc and the secondtarget is tin. Here, a third graded film region is deposited. Thesubstrate is then conveyed through a bay equipped with two tin targets.In these two bays, there is deposited a fourth homogenous film region,which consists essentially of tin oxide. Next, the substrate is conveyedthrough a bay in which the first target is tin and the second target iszinc. Here, a fourth graded film region is deposited. Finally, thesubstrate is conveyed through two sputtering bays each equipped with twozinc targets, whereby the outermost area of the middle coat is depositedas a fifth homogenous film region, which consists essentially zincoxide.

Thus, the substrate is not exposed to any abrupt changes in thecomposition of the flux to which it is exposed when conveyed through thesputtering line. It will be appreciated that FIG. 4 only depicts part ofthe sputtering line or coater through which the substrate is conveyed.The line or coater includes other sputtering bays (not shown in FIG. 4)in which the remaining portions of the coating 40 are deposited.Sputtering lines and coaters are well known and therefore certainconventional details (e.g., the rollers or other substrate support, thebottom of the coater, etc.) are not illustrated here.

FIG. 5A depicts one particular sputtering apparatus that can be used todeposit a concentration-modulated inner coat 30. This arrangement ofsputtering targets can be used, for example, to produce a middle coathaving the following structure: tin oxide→zinc oxide→tin oxide→zincoxide. Here, the substrate is conveyed through a sputtering bay in whichthe first target is tin and the second target is zinc. Next, thesubstrate is conveyed through a bay in which the first target is zincand the second target is tin. The substrate is then conveyed through abay in which the first target is tin and the second target is zinc.Finally, the substrate is conveyed through a bay in which the firsttarget is zinc and the second target is tin.

It is to be understood that the films stacks depicted in the tables ofthis disclosure are not required to consist only of the illustratedfilms. Rather, other films can be interposed among (e.g., between,beneath, and/or over) the illustrated films. Thus, the films in thetables are in a sequence, though not necessarily a contiguous sequence.In preferred embodiments, though, the illustrated films are in acontiguous sequence. Further, the tables denote silverinfrared-reflective layers 50, 150, although it is to be understood thatother reflective materials can be used. In addition, the tabulatedcoatings are denoted as including blocker layers, although the blockerlayers are not strictly required. For purposes of this particulardisclosure, the blocker layer 80 when provided is not considered to bepart of the middle coat 90, nor is the blocker layer 180 when providedconsidered to be part of the outer coat 70. Preferably, when the blockerlayers are provided, each blocker layer is not a homogenous dielectriclayer, but rather has a metallic inner area and a dielectric outer area.Absent an express indication to the contrary, the thicknesses reportedherein are physical thicknesses, rather than optical thicknesses. Theterms “substantially continuously decreasing concentration”,“substantially continuously increasing concentration”, and the like areused herein to refer to a transition, with increasing distance from thesubstrate, from one dielectric material to another, wherein thetransition occurs over the thickness of the graded film region, ratherthan at a discrete interface where one material changes abruptly toanother. Each such transition is preferably, though not necessarily, agradual transition. In the disclosed embodiments involving zinc tinoxide film, the tin atoms may, for example, account for less than about5-10 atomic percent relative to all the metal atoms in the film. Withrespect to the aluminum in the disclosed zinc aluminum film, thealuminum atoms may, for example, account for less than about 2 atomicpercent relative to all the metal atoms in the film.

While preferred embodiments of the present invention have beendescribed, it should be understood that numerous changes, adaptations,and modifications can be made therein without departing from the spiritof the invention and the scope of the appended claims.

What is claimed is:
 1. A method of producing coated substrates, themethod comprising: a) providing a sputtering line including at leastthree adjacent sputtering bays each adapted for depositing dielectricfilm and each containing a reactive sputtering atmosphere, at least oneof said bays being a transition bay equipped with two or more sputteringtargets of which at least two carry different sputterable materials,wherein the first target in the transition bay carries the samesputterable material as the last or only target in a preceding bay, andwherein the last target in the transition bay carries the samesputterable material as the first or only target in a subsequent bay,wherein all of the targets in the transition bay share the reactivesputtering atmosphere; and b) conveying a substrate through saidsputtering line over rollers defining a path of substrate travel fromone bay to the next and sputtering said targets to deposit upon thesubstrate a coating comprising a graded film region, wherein the gradedfilm region is deposited as a film comprising a substantiallycontinuously decreasing concentration of a first dielectric material anda substantially continuously increasing concentration of a seconddielectric material, wherein the first and second dielectric materialsare different materials having refractive indexes that are substantiallythe same such that the first graded film region transitions from onedielectric material having a given refractive index to anotherdielectric material having substantially the same refractive index toprovide a coating sputtered from said targets in said three adjacentbays having a substantially homogenous refractive index.
 2. The methodof claim 1 wherein the sputterable materials are metals.
 3. The methodof claim 1 wherein said refractive index is between about 1.9 and about2.2.
 4. A method of producing coated substrates, the method comprising:a) providing a sputtering line including at least three adjacentsputtering bays each adapted for depositing dielectric film and eachcontaining a reactive sputtering atmosphere, at least one of said baysbeing a transition bay equipped with two or more metallic targets ofwhich at least two carry different sputterable metals, wherein the firsttarget in the transition bay carries the same sputterable metal as thelast or only target in a preceding bay, and wherein the last target inthe transition bay carries the same sputterable metal as the first oronly target in a subsequent bay, wherein all of the targets in thetransition bay share the reactive sputtering atmosphere; and b)conveying a substrate through said sputtering line over rollers defininga path of substrate travel from one bay to the next and sputtering saidmetallic targets in a reactive oxidizing atmosphere to deposit upon thesubstrate a coating comprising a graded film region, wherein the gradedfilm region is deposited as a film comprising a substantiallycontinuously decreasing concentration of a first dielectric material anda substantially continuously increasing concentration of a seconddielectric material, wherein the first and second dielectric materialsare different materials having refractive indexes that are substantiallythe same such that the first graded film region transitions from onedielectric material having a given refractive index to anotherdielectric material having substantially the same refractive index toprovide a coating sputtered from said targets in said three adjacentbays having a substantially homogenous refractive index.
 5. The methodof claim 4 wherein the first target comprises tin and the second targetcomprises zinc.
 6. The method of claim 4 wherein the three adjacentsputtering bays include a first sputtering bay, a second transitionsputtering bay, and a third sputtering bay, wherein the first sputteringbay includes two targets comprising tin, the second transitionsputtering bay includes a first target comprising tin and a secondtarget comprising zinc, and the third sputtering bay includes twotargets comprising zinc.
 7. The method of claim 4 wherein the firsttarget comprises zinc and the second target comprises tin.
 8. The methodof claim 4 wherein the three adjacent sputtering bays include a firstsputtering bay, a second transition sputtering bay, and a thirdsputtering bay, wherein the first sputtering bay includes two targetscomprising zinc, the second transition sputtering bay includes a firsttarget comprising zinc and a second target comprising tin, and the thirdsputtering bay includes two targets comprising tin.
 9. The method ofclaim 4 wherein the three adjacent sputtering bays include a firstsputtering bay including two targets comprising zinc, a secondsputtering bay including two targets comprising zinc, a third transitionsputtering bay including a first target comprising zinc and a secondtarget comprising tin, a fourth sputtering bay including two targetscomprising tin, a fifth transition sputtering bay comprising a firsttarget comprising tin and a second target comprising zinc, a sixthsputtering bay including two targets comprising zinc, a seventhsputtering bay including two targets comprising zinc, an eighthtransition sputtering bay including a first target comprising zinc and asecond target comprising tin, a ninth sputtering bay including twotargets comprising tin, a tenth transition sputtering bay including afirst target comprising tin and a second target comprising zinc, aneleventh sputtering bay including two targets comprising zinc, and atwelfth sputtering bay including two targets comprising zinc.